The human perception of depth in a visual scene arises largely through the differences between the images observed by the left and right eyes. The term for this difference is “binocular disparity,” and (together with accommodation cues) it is responsible for much of our acuity in determining the range to objects within approximately ten meters of us.
Several artificial approaches for determining the range to an object also involve the disparity signal between two or more well-aligned cameras (or captures from a moving camera—see below) or light sources. In these, typically one or more focusing lenses estimate the location of marker points, which may be intrinsic features of the scene (in the case of passive binocular disparity measurement) or may be high-texture patterns (often in near infrared) projected onto the scene. Accurate angular measurements of the scene yield information about the depth to an object. In some cases, a single moving camera can use data from different latencies to establish depth from disparity.
Binocular disparity sensors are not yet ubiquitous, in part due to their limited accuracy and their manufacturing complexity, especially the alignment and calibration needed to make accurate disparity measurements.